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Strongly screening β decay antineutrino energy loss in presupernova
Jing-Jing Liu, Dong-Mei Liu, Liang-Huan Hao
Published:   , doi: 10.1088/1674-1137/43/6/064107
In this paper we investigate the ion-ball screening model (model (I)), which is focused on the screening electrostatic potential per electron under the Wigner-Seitz approximation and the Q-value correction. By considering the changes of the Coulomb free energy and the effects of strong electron screening (SES) on the Q-value and the Coulomb chemical potential, we discuss the linear-response screening model (model (II)). We also analyze the influence of the SES on the \begin{document}$ \beta^- $\end{document} decay antineutrino energy loss rate by considering the corrections of the Q-value, the electron chemical potential and electron energy, and shell and pair effects. It is found that the antineutrino energy loss rate increases by two orders of magnitude (e.g., the SES enhancement factor can get to 651.9 for model (II)), due to the SES effect.
Constraining the symmetry energy at subnormal density by the isovector giant dipole resonances of spherical nuclei
Jun Su
Published:   , doi: 10.1088/1674-1137/43/6/064109
The deducing Langevin equation has been applied to investigate the isoscalar giant monopole resonance in our previous work. In this work, the framework is extended to study the isovector giant dipole resonance (IVGDR). The potential well in the IVGDR is calculated by separating the neutron and proton densities based on the Hartree-Fock ground state. Then the Langevin equation is solved self-consistently, resulting in the centroid energy of the IVGDR without width. It is found that the symmetry energy around the density 0.02 fm−3 contribute the most to the potential well in the IVGDR. Comparing to the updated experimental data of IVGDR energies in the spherical nuclei, the calculations within 37 sets of Skyrme functionals suggest the symmetry energy from 8.13 to 9.54 MeV at density 0.02 fm−3.
Monte Carlo simulation of post-fission process for fast neutron-induced 237Np fission
Chang-Qi Liu, Zheng Wei, Chao Han, Chang Huang, Zhi-Wu Huang, Zhan-Wen Ma, Shuang-Jiao Zhang, Shao-Hua Peng, Wei-Min Li, Xiao-Hou Bai, Jun-Run Wang, Xiao-Long Lu, Yu Zhang, Da-Peng Xu, Xiao-Dong Su, Ze-en Yao
Published:   , doi: 10.1088/1674-1136/43/6/064001
The developed potential-driving model can describe the driving potential distribution and well reproduce the pre-neutron emission mass distributions at different incident energies for \begin{document}$ {}^{237} \rm{Np(n,f)} $\end{document} reaction. The potential-driving model is implanted in Geant4, and based on the potential-driving model, it can calculate the fission-fragments yields distributions, kinetic energy distributions, fission neutron spectrum and fission total nubar for \begin{document}$ {}^{237} \rm{Np(n,f)} $\end{document} reaction with reasonable. Compared with built-in G4ParaFissionModel, the calculated results from the potential-driving model are in agreements with experimental data and evaluated data. Given the good agreement with experimental data, the potential-driving model in Geant4 can well describe the post-fission process for neutron-induced actinide nuclei fission, which is very important for the study of neutron-transmutation physics and will guide the physical design of transmutation physics system.
Study of $ a_1$ (1260) in the reaction of $ \gamma p \to \pi^+\pi^+\pi^- n $
Xu Zhang, Ju-Jun Xie
Published:   , doi: 10.1088/1674-1137/43/6/064104
Within an effective Lagrangian approach and resonance model, we study the \begin{document}$ \gamma p \to a_1(1260)^+ n $\end{document} and \begin{document}$ \gamma p \to \pi^+\pi^+\pi^- n $\end{document} reactions via the \begin{document}$ \pi $\end{document}-exchange mechanism. For the \begin{document}$ \gamma p \to \pi^+\pi^+\pi^- n $\end{document} reaction, we perform a calculation for the differential and total cross sections by considering the contributions of the \begin{document}$ a_1(1260) $\end{document} intermediate resonance decaying into \begin{document}$ \rho \pi $\end{document} then into \begin{document}$ \pi^+\pi^+\pi^- $\end{document}. Besides, the non-resonance process is also considered. With a lower mass of \begin{document}$ a_1(1260) $\end{document}, the experimental data for the invariant \begin{document}$ \pi^+\pi^+\pi^- $\end{document} mass distributions can be fairly well reproduced. For the \begin{document}$ \gamma p \to a_1(1260)^+ n $\end{document} reaction, with the model parameters, the total cross section is of the order of 10 \begin{document}$ \mu $\end{document}b at photon beam energy \begin{document}$ E_{\gamma} $\end{document}~2.5 GeV. It is expected that the model calculations in this work could be tested by future experiments.
Computation of products of phase space factors and nuclear matrix elements for the double beta decay
S. Stoica
Published:   , doi: 10.1088/1674-1137/43/6/064108
The nuclear matrix elements (NME) and phase space factors (PSF) entering the half-life formulas of the double-beta decay (DBD) process are two key quantities whose accurate computation still represents a challenge. In this paper we propose a new approach of calculating them, namely to compute directly their product as an unique formula. This procedure allows a more coherent treatment of the nuclear approximations and input parameters appearing in both quantities and avoids possible confusion in interpreting the DBD data due to different individual expressions adopted for PSF and NME (and consequently their reporting in different units) by different authors. Our calculations are performed for both two neutrino (\begin{document}$ 2\nu\beta\beta $\end{document}) and neutrinoless (\begin{document}$ 0\nu\beta\beta $\end{document}) decay modes, and for five nuclei of most experimental interest. Further, using the most recent experimental limits for \begin{document}$ 0\nu\beta\beta $\end{document} decay half-lives, we provide new constraints on the light mass neutrino parameter. Finally, by separating in the half-lives formulas the factor representing the axial-vector constant to the forth, we advance suggestions on how to reduce the errors introduced in calculation by the uncertain value of this constant by exploiting the DBD data from different isotopes and/or decay modes.
High-K isomer and the rotational properties in the odd-Z neutron-rich nucleus 163Eu
Xiao-Tao He, Ze-Long Chen
Published:   , doi: 10.1088/1674-1137/43/6/064106
The newly observed isomer and the ground-state band in odd-Z neutron-rich rare-earth nucleus 163Eu are investigated by using the cranked shell model (CSM) with pairing treated by a particle-number conserving (PNC) method. This is the first time the detailed theoretical investigations are performed on the observed 964(1) keV isomer and the ground-state rotational band in 163Eu. The experimental data are reproduced very well by the theoretical results. The configuration of the 964(1) keV isomer is assigned as the three-particle \begin{document}$\displaystyle\frac{13}{2}^{-}\left(\nu\displaystyle\frac{7}{2}^{+}[633]\otimes\nu\displaystyle\frac{1}{2}^{-}[521]\otimes\pi\displaystyle\frac{5}{2}^{+}[413]\right)$\end{document} state. More low-lying multi-particle states are predicted in 163Eu. Due to its significant effect on the nuclear mean field, the high-order \begin{document}$\varepsilon_{6}$\end{document} deformation plays an important role in the state energies and the configuration assignment of the multi-particle states. Comparing to its neighboring even-even nuclei 162Sm and 164Gd, there is a 10%~15% increase in \begin{document}$J^{(1)}$\end{document} of the one-particle ground-state band in 163Eu. This is explained by the pairing reduction due to the blocking of the nucleon on the proton \begin{document}$\pi\displaystyle\frac{5}{2}^{+}$\end{document}[413] orbital in 163Eu.
Production of the exotic neutron-deficient isotopes near N, Z = 50 in multinucleon transfer reactions
Xin-Xin Xu, Gen Zhang, Jing-Jing Li, Bing Li, Cheikh A. T. Sokhna, Xin-Rui Zhang, Xiu-Xiu Yang, Shi-Hui Cheng, Yu-Hai Zhang, Zhi-Shuai Ge, Cheng Li, Zhong Liu, Feng-Shou Zhang
Published:   , doi: 10.1088/1674-1137/43/6/064105
The multinucleon transfer reaction in the collisions of 40Ca+124Sn at \begin{document}$ E_{ \rm{c.m.}}=128.5 $\end{document} MeV is investigated by using the improved quantum molecular dynamics model. The measured angular distributions and isotopic distributions of the products are reproduced reasonably well by the calculations. The multinucleon transfer reactions of 40Ca+112Sn, 58Ni+112Sn, 106Cd+112Sn, and 48Ca+112Sn are also studied. It shows that the combinations of neutron-deficient projectile and target are advantageous to produce the exotic neutron-deficient nuclei near N, Z = 50. The charged particles emission plays an important role at small impact parameters in the deexcitation processes of the system. The production cross sections of the exotic neutron-deficient nuclei in multinucleon transfer reactions are much larger than those measured in the fragmentation and fusion-evaporation reactions. Several new neutron-deficient nuclei can be produced in 112Cd+Sn reaction. The corresponding production cross sections for the new neutron-deficient nuclei, 101, 112Sb, 103Te, and 106, 107I, are 2.0 nb, 4.1 nb, 6.5 nb, 0.4 \begin{document}$ \mu $\end{document}b and 1.0 \begin{document}$ \mu $\end{document}b, respectively.
Chiral phase transition from the Dyson-Schwinger equations in a finite spherical volume
Ya-Peng Zhao, Rui-Rui Zhang, Han Zhang, Hong-Shi Zong
Published:   , doi: 10.1088/1674-1137/43/6/063101
Within the framework of Dyson-Schwinger equations and by means of Multiple Reflection Expansion, we study the finite volume effects on the chiral phase transition in a sphere, especially discuss its influence on the location of the possible critical end point (CEP). According to our calculations, when we take the sphere instead of cube as a research, the influence of finite volume effects on phase transition is not as significant as previously calculated. For instance, as the radius of spherical volume decreases from infinite to 2 fm, at zero chemical potential and finite temperature, the critical temperature \begin{document}$T_{c}$\end{document} has only a slight drop. And at finite chemical potential and finite temperature, the location of CEP shifts toward smaller temperature and higher chemical potential, but the amplitude of variation does not exceed 20%. So we find that not only the size of the volume, but also the shape of the volume will have a considerable impact on the phase transition.
Photoproduction of J/$ \psi $ in non-single-diffractive p+p collisions
Ze-Hua Cao, Li-Juan Ruan, Ze-Bo Tang, Zhang-Bu Xu, Chi Yang, Shuai Yang, Wang-Mei Zha
Published:   , doi: 10.1088/1674-1137/43/6/064103
Recently, significant enhancements of J/\begin{document}$ \psi $\end{document} production at very low transverse momenta were observed by the ALICE and STAR collaboration in peripheral hadronic A+A collisions. The anomaly excesses point to evidence of coherent photon-nucleus interactions in violent hadronic heavy-ion collisions, which were conventionally studied only in ultra-peripheral collisions. Assuming that the coherent photoproduction is the underlying mechanism which is responsible for the excess observed in peripheral A+A collisions, its contribution in p+p collisions with nuclear overlap, i.e. non-single-diffractive collisions, is of particular interest. In this paper, we perform a calculation of exclusive J/\begin{document}$ \psi $\end{document} photoproduction in non-single-diffractive p+p collisions at RHIC and LHC energies base on the pQCD motivated parametrization from world-wide experimental data, which could be further employed to improve the precision of phenomenal calculations for photoproduction in A+A collisions. The differential rapidity and transverse momentum distributions of J/\begin{document}$ \psi $\end{document} from photoproduction are presented. In comparison with the J/\begin{document}$ \psi $\end{document} production from hadronic interactions, we find that the contribution of photoproduction is negligible.